This invention relates to a method for calcium fortification of soy milk producing calcium levels equal to or greater than the calcium level found in bovine milk while preventing curdling of the milk proteins.
Soy milk is a water extract of soybeans which has been found to be nutritionally comparable to cow's milk in most respects. Since soy milk does not contain lactose and has no cholesterol, it is an ideal substitute for cow's milk for lactose-intolerant individuals and those on restricted cholesterol intake diets. Additionally, if problems pertaining to production and storage can be solved soy milk could provide an inexpensive and readily available protein source for individuals in developing nations.
Methods of extracting soy milk from the soybean are well known. Widespread acceptance of soy milk as a substitute for cow's milk has not been forthcoming because conventionally prepared soy milk is inferior to the conventional bovine milk in taste and in some nutritional aspects. Conventionally prepared soy milk contains approximately 12 percent of the available calcium found in bovine milk. Individuals substituting soy milk for bovine milk must supplement their calcium intake from other sources. Furthermore, conventionally prepared pasteurized soy milk is highly susceptible to bacterial growth and has an extremely short shelf life, which limits its dietary usefulness. Subjective factors have also prevented public acceptance of soy milk. Traditionally prepared soy milk may have a distinct odor and taste which differs from conventional cow's milk. The odor and taste have made soy milk less desirable than traditional bovine milk.
Attempts to fortify soy milk with additional calcium have been unsuccessful. Previous attempts to provide a stable soy milk having elevated calcium levels have resulted in coagulation and precipitation of soy protein via a protein-ionic calcium interaction.
Various chemicals have been employed to chelate calcium ions and prevent soy protein precipitation. Among these chemicals are citrates such as calcium citrate, ethylene diamine tetraacetic acid (EDTA) and alkali phosphates. U.S. Pat. Nos. 1,210,667 and 1,265,227 teach beverages containing calcium carbonate or calcium chloride as the calcium ion source and sodium phosphate as the chelating agent. Weingartner, et al proposes calcium citrate as a chelating agent (48 J. Food Sci. 256-263 (1983)). Hirotsuka, et al proposes a process which employs sonication of lecithin in a solution containing EDTA to envelope the calcium ions present in solution (49 J. Food Sci. 1111-1112, 1127 (1984)). These methods either do not yield a soy milk having calcium levels equal to or greater than bovine milk or require several complex steps impractical in general application. Several of the chelating agents previously employed reduce the bioavailability of the calcium ions in solution in the milk. Thus, while total calcium ion concentration in the milk may be increased dramatically over unfortified soy milk, a large portion of the added calcium remains nutritionally unavailable. Further, current methods yield a soy milk which is readily susceptible to bacterial growth unless sterilized.
Thus, it is desirable to provide a method for fortifying soy milk with calcium so that the soy milk has a calcium level equal to or greater than that found in bovine milk without coagulation of the soy protein and calcium. It is further desirable to employ agents to prevent coagulation which will provide minimal decrease in the bioavailability of the calcium present in the soy milk. It is also desirable to employ agents which will provide a bacteriostatic effect thereby increasing the resistance of the soy milk to bacterial growth. It is also desirable that these additives be either tasteless or aid in imparting a pleasant taste and odor to the soy milk.